1. Field of the Invention
This invention relates to a nickel, chromium, iron, molybdenum, niobium, welding alloy, articles made therefrom for use in producing weldments, and weldments and methods for producing these weldments.
2. Description of Related Art
Heretofore, in various welding applications, including equipment used in nuclear power generation, weldments are required that provide resistance to various cracking phenomenon. This includes not only intergranular stress corrosion cracking (“IGSCC”) but hot-cracking, cold cracking (DDC), and root cracking as well.
During the lives of commercial and military nuclear power generation equipment, the nuclear industry has replaced the first generation of nickel alloys that had only 14-15% chromium with a family that now contains about 30% chromium. This family of alloys is virtually immune to IGSCC, but other issues have been discovered about the welding products of the same family. The initial 30% chromium welding products (UNS N06052) contain about 0.50% Al and 0.50% Ti and have reasonably good general weldability. However, the aluminum content nearly always contributes to floating oxide impurities on many of the weld beads in spite of scrupulous efforts to provide excellent gas shielding. These oxides, if not removed by grinding, will often find their way into the interior of multi-pass welds and appear as inclusions which are detectable by radiography or ultrasonic inspection methods. This condition is unacceptable when encountered during the repair of operating nuclear plant components that are radioactively “hot”. In addition, deposits made using these welding products are susceptible to ductility-dip cracking (“DDC”).
A new family of 30% chromium nickel alloy welding products was introduced early in the 21st century that addressed these issues. This alloy family (UNS N06054) exhibited reduced aluminum and titanium contents and had additions of boron, zirconium and niobium. These products were capable of producing very clean weld deposits without the floating oxide impurities of the previous family. In addition, they provided improved resistance to DDC, but under conditions of unfavorable bead shape and very high heat input per unit volume of weld metal added, occasional DDC fissures were found. This family also exhibited resistance to “root cracking” and solidification cracking as described in U.S. Pat. No. 6,242,113 to Kiser.
The present invention overcomes the shortcomings of the prior art by providing a nickel, chromium, iron, molybdenum, niobium welding alloy and weldments made therefrom that provide the desired strength and corrosion resistance in addition to resistance to solidification cracking, DDC, root cracking, as well as stress corrosion cracking. Additionally, the present invention provides a welding alloy of the nickel, chromium, iron, molybdenum, niobium type in a variety of forms that is particularly adapted for uses in fabricating and repair of equipment used in nuclear power generation.